Method of forming secondary electron emission preventing layer for post-deflection acceleration type color picture tube

ABSTRACT

A method of forming a secondary electron emission preventing layer for a post-deflection acceleration type color picture tube, wherein a layer made of a mixture consisting of particles of a secondary electron emission preventing material, an organic binder and fine metal grains is formed on those surfaces of constituting parts inside the tube, at least a shadow mask, on which primary electrons impinge, or an inorganic binder layer made of an inorganic compound is formed on the surfaces and a mixed layer of particles of a secondary electron emission preventing material and an organic binder is formed on the inorganic binder layer, or the surfaces of the constituting parts are roughened and a mixed layer of particles of a secondary electron emission preventing material and an organic binder is formed on the roughened surfaces, the organic binder being thereafter burnt away by heat treatment. Alternatively, a mixed layer of an inorganic binder consisting of an inorganic compound and particles of a secondary electron emission preventing material is formed on the surfaces and a surface layer made of the secondary electron emission preventing material is formed on the mixed layer.

United States Patent [191 Misumi et a].

[ 1 Mar. 25, 1975 [75] Inventors: Akira Misumi; Toshiaki Kasai;

Kenji F ukuda; Hiromitu Nakai, all of Mobara, Japan [73] Assignee:Hitachi, Ltd., Tokyo, Japan [22] Filed: Sept. 7, 1972 [21] Appl. No.:286,948

[30] Foreign Application Priority Data Sept. 8, 1971 Japan 46-68891Sept. 8, 1971 Japan 46-68892 Sept. 8, 1971 Japan 46-68893 Sept. 8, 1971Japan 46-68895 [52] US. Cl. 117/46 CA, 117/70 S, 117/71 R, 117/71 M,ll7/2l6, 313/85 S, 313/92 B, 313/106 [51] Int. Cl. C230 1l/00, B44d H44[58] Field of Search 117/46 CA, 46 CB, 71 R, 117/70 S, 71 M, 216;313/106, 92 B, 85 S [56] References Cited UNITED STATES PATENTS2,518,434 8/1950 Lubszynski 117/71 2,829,295 4/1958 Gast et al 2,942,1306/1960 Sheldon 3,010,092 11/1961 Caddock.... 3,093,501 ll/1963 Clayton3,475,639 10/1969 Driffort et a1 313/106 3,600,213 8/1971 Amdt 313/85 S3,604,970 9/1971 Culberton et al 117/216 3,703,401 11/1972 Deal et al.117/216 Primary Examiner-William D. Martin Assistant Examiner-Janyce A.Bell Attorney, Agent, or FirmCraig & Antonelli [57] ABSTRACT A method offorming a secondary electron emission preventing layer for apost-deflection acceleration type color picture tube, wherein a layermade of a mixture consisting of particles of a secondary electronemission preventing material, an organic binder and fine metal grains isformed on those surfaces of constituting parts inside the tube, at leasta shadow mask, on which primary electrons impinge, or an inorganicbinder layer made of an inorganic compound is formed on the surfaces anda mixed layer of particles of a secondary electron emission preventingmaterial and an organic binder is formed on the inorganic binder layer,or the surfaces of the constituting parts are roughened and a mixedlayer of particles of a secondary electron emission preventing materialand an organic binder is formed on the roughened surfaces, the organicbinder being thereafter burnt away by heat treatment. Alternatively, amixed layer of an inorganic binder consisting of an inorganic compoundand particles ofa secondary electron emission preventing material isformed on the surfaces and a surface layer made of the secondaryelectron emission preventing material is formed on the mixed layer.

12 Claims, 10 Drawing Figures PATENTEDHAR25I975 3,873,343 sum 1 g5 g r 2qoos goas aswo ACCELERATION VOLTAGE (V) .3 3 G o. h %m mmmmw. 2, F o .8o

. 4 95m zommiw 58mm PATENTEDH 5 I975 snzileq g FIG FIG

FIG

, 05E zowwsm 58mm I000 ACCELERATION VOLTAGE (v) PATENTED MR2 5 I975SHEET 3 0F 4 F'IG 5 OE. zgwgsm m 96uwm s oos oa a a ooo ACCELERATIONVOLTAGE V PATENTED 3. 873 343 saw u p g SECONDARY EMISSION RA'HO (8) 25000 20000 ACCELERATION VOLTAGE (v) METHOD OF FORMING SECONDARY ELECTRONEMISSION PREVENTING LAYER FOR POST-DEFLECTION ACCELERATION TYPE COLORPICTURE TUBE The present invention relates to a post-deflectionacceleration type color picture tube, and more particularly to a methodof forming a secondary electron emission preventing layer thereof.

In the field of the post-deflection acceleration type color picturetube, it has hitherto been suggested to form a secondary electronemission preventing layer on the inner wall of a glassenvelope of thecolor picture tube, the surface of a shadow mask or the surface of anyother component on which primary electrons impinge, and to therebyprevent deterioration in color purity of a picture. A prior-artsecondary electron emission preventing layer for the post-deflectionacceleration type color picture tube has been formed in such a way thata mixed layer which consists of a secondary electron emission preventingmaterial such as graphite particles and an inorganic binder, such aswater glass, not being burnt away by heat treatment in the manufactureof the tube and having the function of the binder even after completionof the tube is provided on, e.g., the surface of the shadow mask.

With such a secondary electron emission preventing layer, since theinorganic binder covers the surfaces of the particles of the secondaryelectron emission preventing material and the surface of the secondaryelectron emission preventing layer in the form of a thin film, a filmhaving a strong adhesive force is obtained. On the other hand, however,the seeondary'eleetron emission preventing effect decreases, and thefunction of the secondary electron emission preventing layer cannot besatisfactorily accomplished. This is attributable to the fact that,since the secondary emission ratio of the layer of the inorganic binderof water glass or the like covering the secondary electron emissionpreventing material is generally large, the number of secondaryelectrons generated on the inorganic binder layer becomes large, withthe result that the number of secondary electrons emitted from theentire secondary electron emission preventing layer becomes large.

Accordingly, in order to reduce the ratio of the secondary emission fromthe secondary electron emission preventing layer, it has been tried toform a secondary electron emission preventing layer using as the binder,for example, only an organic binder which burns away by the heattreatment in the manufacture of the tube. In the trial, the secondaryelectron emission preventing layer has been formed in' such a mannerthat a suspension of the organic binder and particles of the secondaryelectron emission preventing material is sprayed by the conventionalspraying method, and that the organic binder is burnt away by the heattreatment in the tube manufacturing process. The secondary electronemission preventing layer thus obtained, however. is not practical inbeing of a small adhesive force and being very liable to exfoliate.

An object of the present invention is to provide a method of forming asecondary electron emission preventing layer which is greatly effectiveto prevent the secondary emission.

Another object of the present invention is to provide a method offorming a secondary electron emission preventing layer according towhich, not only the strength of the secondary electron emissionpreventing layer itself, but also the adhesive force of the secondaryelectron emission preventing layer with the surface of a member on whichit is provided is increased.

The above and other objects, features and advantages of the inventionwill become more apparent from the following description havingreference to the accompanying drawings, in which:

FIG. 1 is a sectional view for explaining a prior-art method of forminga secondary electron emission preventing layer for a post-deflectionacceleration type color picture tube;

FIG. 2 is a sectional view for explaining a method of forming asecondary electron emission preventing layer for a post-deflectionacceleration type color picture tube and according to the presentinvention;

FIG. 3 is a diagram showing secondary electron emission ratio for thesecondary electron emission preventing layer formed by the method inFIG. 2, in comparison with that for the layer by the prior art method ofFIG. 1;

FIGS. 4 and 5 are sectional views for explaining methods of forming asecondary electron emission preventing layer for a post-deflectionacceleration type color picture tube and according to furtherembodiments of the present invention;

FIG. 6 is a diagram similar to FIG. 3 showing secondary electronemission ratio for the secondary electron emission preventing layersformed by the methods in FIGS. 4 and 5;

FIG. 7 is a sectional view for explaining a method of forming asecondary electron emission preventing layer for a post-deflectionacceleration type color picture tube and according to a still furtherembodiment of the present invention;

FIG. 8 is a diagram similar to FIG. 3 showing secondary electronemission ratio for the secondary electron emission preventing layerformed by the method in FIG. 7;

FIG. 9 is a sectional view for explaining a method of forming asecondary electron emission preventing layer for a post-deflectionacceleration type color picture tube and according to a yet furtherembodiment of the present invention; and

FIG. 10 is a diagram similar to FIG. 3 showing secondary electronemission ratio for the secondary electron emission preventing layerformed by the method in FIG. 9.

FIG. I illustrates a prior-art method of forming a secondary electronemission preventing layer for a postdeflection acceleration type colorpicture tube. Referring to the figure, numeral 1 designates a componentor member, such as a shadow mask, on which the secondary electronemission preventing layer is formed. Shown at 2 is the secondaryelectron emission preventing layer which is composed of a mixed layer ofa secondary electron emission preventing material 3 such as graphiteparticles and an inorganic binder 4. such as water glass, not beingburnt off by heat treatment in the manufacture of the tube and keepingthe function of the binder after completion of the tube. The secondaryelectron emission preventing layer 2 is formed on the surface of themember I.

Such a secondary electron emission preventing layer 2 is advantageous inbecoming a film with a strong adhesive force, since the inorganic binder4 fully covers the surfaces of the particles 3 of the secondary electronemission preventing material and the surface of the secondary electronemission preventing layer 2 in the form of the thin film. On the otherhand, the secondary electron emission preventing effect exhibits atendency as illustrated at a curve in FIG. 3, and the function as thesecondary electron emission preventing layer is not sufficientlyattained. This is considered to come from the fact that, since thesecondary emission ratio (8) of the layer of the inorganic binder, suchas water glass, covering the secondary electron emission preventingmaterial 3 is generally large, the number of secondary electrons createdby the inorganic binder layer becomes large, resulting in a large numberof secondary electrons ejected from the whole secondary electronemission preventing layer 2.

Accordingly, to the end of diminishing the secondary emission ratio ofthe secondary electron emission preventing layer, it has been tried toform a secondary electron emission preventing layer using as the binder,for example, only an organic binder which burns off by the heattreatment in the manufacture of the tube. More specifically, thesecondary electron emission preventing layer has been formed in such away that a suspension of the organic binder and the particles of thesecondary electron emission preventing material is sprayed by theconventional spraying method, and that the organic binder is burnt offby the heat treatment in the tube producing process. The secondaryelectron emission preventing layer formed in this way, however, has beenweak in the bonding power among the particles of the secondary electronemission preventing material, and has been very easily exfoliated.

When, herein, the secondary electron emission preventing material hasbeen made of fine particles being less than several microns in theparticle size, there has been obtained the film of a secondary electronemission preventing layer which is increased in the bonding power amongthe particles and which has a sufficient bonding strength even after thebaking. With a film thickness enough to prevent the secondary emission,however, although the film is strong in the bonding power among theparticles of the secondary electron emission preventing material, it isweak in the adhesive force between the particles of the secondaryelectron emission preventing material and the substrate or member onwhich the film is formed. A phenomenon in which the film exfoliates fromthe substrate has therefore occurred.

The present invention will be described hereunder with reference toFIGS. 2 to 10. In these figures, the same numerals are assigned to thesame elements of the construction of the invention or necessary forexplaining the invention.

FIG. 2 is a sectional view for explaining a method according to anembodiment of the present invention, for forming a secondary electronemission preventing layer for use in a post-deflection acceleration typecolor picture tube. In the figure, numeral I designates a member insidethe tube, such as a shadow mask, on which the secondary electronemission preventing layer is formed. Numeral 7 indicates a mixed layerof particles 3 ofa secondary electron emission preventing material, finegrains 5 of a metal, and an organic binder 6. The mixed layer 7 isprovided on that surface of the member inside the tube on which primaryelectrons impinge, for example, on the surface of the shadow mask on theelectron gun side. The secondary electron emission preventing layer isformed, by way of example, as below.

In order to increase the adhesive force of the secondary electronemission preventing layer to-be-formed, the fine metal grains 5, such assilver powder, being 1 ,u. or less in the grain diameter are added to asuspension of the organic binder 6 and the secondary electron emissionpreventing material 3 such as graphite to the amount of several percentby weight with respect to the secondary electron emission preventingmaterial in the suspension. Using the suspension added with the metalpowder, the mixed layer 7 is made on, e.g., the surface of the shadowmask on the electron gun side by a suitable method such as spraying,coating with a brush, and immersion. Thereafter, the organic binder isburnt away by baking in the production of the tube. Thus, a secondaryelectron emission preventing layer consisting of the secondary electronemission preventing material and the fine grains of the metal is formed.In consideration of a satisfactory secondary emission preventing effectof the secondary electron emission preventing layer to-be-formed, avalue of at least 3 t suffices for the thickness of the mixed layer 7.In consideration of the working property etc., a thickness ofapproximately 5 u to IO ,u is the most effective. The upper limit isapproximately 30 p. in practical use.

With such a process, the fine metal grains 5 included within thesecondary electron emission preventing layer are somewhat sinteredduring the baking. For this reason, the bonding force among theparticles 3 of the secondary electron emission preventing material isincreased, and the strength of the whole secondary electron emissionpreventing layer as well as the adhesive force of the same with thesubstrate I is increased. The film of a strength sufficiently enduringpractical use can accordingly be formed. Besides, in the film of theembodiment, the added fine metal grains 5 amount to several percent orless with respect to the secondary electron emission preventing material3, and are uniformly distributed in the film. For this reason, littleincrease in the secondary electron emission ratio is brought about, andthe film can be satisfactorily put into practical use as the secondaryelectron emission preventing film. In this case, the fine metal grainsare desirably those which are difficult to oxidize in the air and whichare small in the secondary emission ratio. In addition, a smaller grainsize is better. It has been made sure that, when the grain size exceeds1 u, the adhesive force lowers. Yet in addition, the quantity ofaddition of the fine metal grains is determined in consideration of thesecondary emission ratio of the fine metal grains, and generally amountsto several percent or less by weight.

EXAMPLE I To a graphite suspension containing 6.6% by weight of flakegraphite having a particle size of l p. and an organic binder in adispersion medium such as water, 0.04% by weight of silver powder havinga grain size of 0.1 p, is added. The suspension thus prepared is sprayedon the surface of a shadow mask to a thickness of approximately lO p..Thereafter, the organic binder is burnt off by heat treatment in theconventional manufacturing process of the color picture tube. In a mixedlayer obtained in this way as comprises the graphite and the silverpowder, the fine silver powder is interposed among the graphiteparticles to increase the bonding power among the graphite particles. Avery solid film of the secondary electron emission preventing layer isaccordingly formed. In this case, the silver powder increases also theadhesive force between the shadow mask and the graphite particles, toprevent the film of the secondary electron emission preventing layerfrom being exfoliated from the shadow mask.

The secondary emission ratio of the mixed layer of the graphite andsilver powder as constitutes the secondary electron emission preventinglayer thus formed, is shown by a curve 21 in FIG. 3. In comparison withthe secondary emission ratio (at a curve 22) of a secondary electronemission preventing layer employing no fine metal grain, the secondaryemission ratio of the mixed layer is increased only very slightly, andhence, the mixed layer is satisfactorily practicable as the secondaryelectron emission preventing layer. The silver power can also be I p. orbelow in the grain size, and range from 0.01 to 0.5% by weight in theamount of addition. In FIG. 3, the axis of abscissa represents theacceleration voltage (in volts) of primary electrons, while the axis ofordinate the secondary emission ratio (6). The same applies to FIGS. 6,8 and 10.

In the foregoing embodiment, the fine metal grains are directly used asthe metal powder mixed into the particles 3 of the secondary electronemission preventing material. The present invention, however, is notrestricted to such aspect, but fine metal grains may of course beemployed which are obtained in such way that a metallic salt dissolvedin a suitable solvent is added to the graphite suspension, and that thefine metal grains are precipitated from the metallic salt during thebaking in the production of the tube.

FIG. 4 is a sectional view for explaining a method according to anotherembodiment of the present invention, for forming a secondary electronemission preventing layer for use in a post-deflection acceleration typecolor picture tube. In the figure, numeral 8 indicates an inorganicbinder layer formed on the member 1 inside the tube and made of aninorganic compound, such as water glass, which does not burn away by theheat treatment. Shown at 9 is a mixed layer which is formed on theinorganic binder layer 8 and in which the particles 3 of the secondaryelectron emission preventing material and the organic binder 6 aremixed. The secondary electron emission preventing layer is formed, byway of example, as stated below.

In order to prevent the exfoliation phenomenon of the secondary electronemission preventing layer, an inorganic binder consisting of theinorganic compound, such as water glass, which does not burn off even bythe heat treatment is very thinly coated on that surface of the member 1on which primary electrons impinge, for example, the surface of a shadowmask on the electron gun side. Thus, the inorganic binder layer 8 beingI to 2 [L thick is formed. A suspension of the organic binder 6 and theparticles 3 of the secondary electron emission preventing material suchas graphite and not exceeding several microns in the particle size issprayed on the inorganic binder layer 8 by the conventional sprayingmethod, to thereby form the mixed layer 9. Thereafter, the organicbinder 6 is burnt away by the heat treatment, to thereby form asecondary electron emission preventing layer which consists of theinorganic binder layer 8 and the secondary electron emission preventingmaterial.

With such method, even after the organic binder 6 burns away by thebaking in the manufacture of the tube, the secondary electron emissionpreventing layer is sufficiently strong in the bonding among theparticles and in the bonding between the particles and the substrate ormember, and can sufficiently endure practical use. In addition, theinorganic binder having a large secondary emission ratio exists only inthe vicinity of the surface of the member I, so that the secondaryemission ratio of the secondary electron emission preventing layer canbe suppressed to a sufficiently small value by thickly forming the mixedlayer 9.

EXAMPLE 2 Potash water glass at a concentration of 10% by weight issprayed onto the surface of a shadow mask, to form an inorganic binderlayer made of the water glass, having a strong adhesive force, being inthe semidried state and being I to 2 ,u. thick. A suspension of graphiteand an organic binder in water as contains 6.6% by weight of flakegraphite of a particle size of l ,u. is sprayed onto the inorganicbinder layer by means of a spray gun, to form a mixed layer of thegraphite and organic binder and having a thickness of I0 s. Thereafter,the mixed layer is heated by the step of heat treatment in the processof producing the color picture tube, to burn off the organic binder.Then, a secondary electron emission preventing layer consisting of theinorganic binder layer and the graphite layer is formed.

The secondary electron emission preventing layer thus formed, has asufficient strength. In addition, as illustrated at a curve 23 in FIG.6, the secondary electron emission preventing effect of the layer of theembodiment is excellent as compared with that of the prior-art mixedlayer which consists of the inorganic binder and the secondary electronemission preventing material and whose secondary emission preventingcharacteristics are shown at the curve 20. Besides, the curve 23 isquite similar to a characteristic curve in the case of graphite alonewith no inorganic binder layer, although the latter curve is notillustrated. Therefore, the layer of the invention exhibits an excellenteffect of preventing the secondary electron emission.

FIG. 5 is a sectional view for explaining a method of forming asecondary electron emission preventing layer, according to a furtherembodiment of the present invention. In the figure, reference numeral 10represents an inorganic binder layer which is formed on the member 1 andwhich is made of an inorganic binder, such as water glass, not burningoff by heat treatment and fine powder 11 of a material, such as graphiteand silver, not exerting any adverse effect on the picture tube.Reference numeral 9 indicates the mixed layer which is formed on theinorganic binder layer 10 and which consists of the particles 3 of thesecondary electron emission preventing material and the organic binder6. The addition of the fine powder 11 results in a roughened surface ofthe binder layer 10, and thus a stronger adhesion between the member 11and the layer 10 and between the mixed layer 9 and the same can beobtained. Also, the roughened surface lowers secondary electron emissionfrom the inorganic binder layer so that the secondary electron emissionpreventing effect is increased. The secondary electron emissionpreventing layer is formed, by way of example, as below.

In order to prevent the exfoliation phenomenon of the secondary electronemission preventing layer, a mixture consisting of the inorganic bindersolution which does not burn away even by the heat treatment and thefine powder of the material which exercises no evil influence on thepicture tube is previously coated thinly on the member 1 by, e.g., thespraying method, to form the binder layer 10. Thereafter, a suspensionof the particles 3 of the secondary electron emission preventingmaterial such as graphite and of a particle size of several microns orbelow, the suspension containing the organic binder 6, is sprayed by theconventional spraying method, to form the mixed layer 9. Thereafter, theorganic binder is burnt away by the heat treatment, to form a secondaryelectron emission preventing layer.

In accordance with the forming method, even after the organic binder 6is burnt off by the baking in the manufacture of the tube, the secondaryelectron emission preventing layer is sufficient in the bonding amongthe particles and in the bonding between the particles and thesubstrate, and can satisfactorily endure practical use. Since theinorganic binder of a large secondary emission ratio is present only inthe vicinity of the member 1, the secondary emission ratio of thesecondary electron emission preventing layer can be restrained to asufficiently small one if the layer is thickly formed.

EXAMPLE 3 A liquid consisting of potash water glass at a concentrationof 10% by weight and 5% by weight of flake graphite of a particle sizeof 0.3 u in water is sprayed on the surface of the substrate of a shadowmask by means ofa spray gun. An inorganic binder layer having a strongadhesive force, being in the scmidried state and being l to 2 a thick isthus formed. A suspension of graphite and an organic binder in water ascontains 6.6% by weight of flake graphite having a particle size of l p,is sprayed on the inorganic binder layer by means of a spray gun. Amixed layer consisting of the graphite and the organic binder and being7 a thick is thus formed. Thereafter, the mixed layer is heated by thestep of heat treatment in the process of manufacturing the color picturetube, to burn away the organic binder. A secondary electron emissionpreventing layer is thus formed.

The secondary electron emission preventing layer formed in this way, hasa sufficient strength. The secondary emission ratio of the layer isshown by the curve 23 in FIG. 6 as in the secondary electron emissionpreventing layer according to the embodiment in FIG. 4.

As regards the thickness of the mixed layer in the embodiments in FIGS.4 and 5, a value of approximately 3 ,u. is sufficient in view ofasatisfactory secondary electron emission preventing effect, and a valueof approximately 5 to p. is effective in view of the working property,etc. The upper limit of the thickness is approximately 30 u in practicaluse.

FIG. 7 is a sectional view for explaining a method according to a stillfurther embodiment of the present invention, for forming a secondaryelectron emission preventing layer for a post-deflection accelerationtype color picture tube. In the figure, the surface of the member 1 isroughened. The mixed layer 9 of the secondary electron emissionpreventing material 3 and the organic binder 6 is formed on the unevensurface of the member 1.

The secondary electron emission preventing layer is formed, by way ofexample, as stated below.

The surface of the member 1, e.g., the surface of a shadow mask on theelectron gun side is roughened by such method as chemical etching andsand blasting, to make unevenness of the surface ofthc member 1 large. Asuspension of the organic binder 6 and fine powder of the secondaryelectron emission preventing material 3 such as graphite of less thanseveral microns in the particle size is sprayed onto the uneven surface,thereby to coat the suspension on the member 1. Thus, the mixed layer 9is formed. Thereafter, the organic binder is burnt off by heattreatment, to form a secondary electron emission preventing layer on themember 1.

With such a method, even after the organic binder is burnt away by theheat treatment in the process of producing the tube, the secondaryelectron emission preventing layer is strong in its adhesive force withthe member 1. The layer does not exfoliate from the member 1, and can beput into practical use. In addition, since the surface of the member 1is made uneven, the secondary emission preventing effect of the film ofthe secondary electron emission preventing layer formed on the surfaceof the member 1 can be enhanced more.

EXAMPLE 4 The surface of a shadow mask is roughened by sand blasting. Asuspension of an organic binder and 6.6% by weight of flake graphitehaving a particle size of approximately 0.2 p. in water is sprayed onthe roughened surface by a spray gun. Thus, a mixed layer consisting ofthe graphite and organic binder and having a thickness of 10 u isformed. Thereafter, the mixed layer is heated by the step of heattreatment in the process of manufacturing the color picture tube, toburn away the organic binder. A secondary electron emission preventinglayer is thus formed. A curve 24 in FIG. 8 represents the secondaryemission ratio of the secondary electron emission preventing layeraccording to this embodiment, a curve 25 represents the secondaryemission ratio of the prior-art secondary electron emission preventinglayer which is formed similarly to the embodiment but without rougheningthe surface of the substrate, and the curve 20 represents, as in FIGS. 3and 6, the secondary emission ratio of the prior-art secondary electronemission preventing layer formed of the mixed layer of the inorganicbinder and the secondary electron emission preventing material. Thesecondary electron emission preventing layer formed in accordance withthe embodiment in FIG. 7 has a sufficient mechanical strength, and asapparent from the graph, it has a sufficient secondary emissionpreventing effect as compared with the prior-art secondary electronemission preventing layers.

FIG. 9 is a view for explaining a method according to a still furtherembodiment of the present invention, for forming a secondary electronemission preventing layer for a post-deflection acceleration type colorpicture tube. Referring to the figure, the mixed layer 2 which containsthe inorganic binder 4 consisting of an inorganie compound, such aswater glass, not burning away by heat treatment and the particles 3 ofthe secondary electron emission preventing material is formed on themember 1. Numeral l2 designates a surface layer formed on the mixedlayer 2 and made of the particles 3 of the secondary electron emissionpreventing material. The addition of the particles of the secondaryelectron emission preventing material in the layer 2 is for decreasingsecondary electron emission from this layer by roughing the surface ofthe layer 2 as well as by its particular property. The roughened surfaceof the mixed layer also provides a stronger adhesion between the mixedlayer and the surface layer.

The secondary electron emission preventing layer is formed, by way ofexample, as follows. In order to prevent the exfoliation phenomenon ofthe secondary electron emission preventing layer, a mixture whichconsists of the inorganic binder 4 of water glass or the like, notburning away even by the heat treatment, and the particles 3 of thesecondary electron emission preventing material such as graphite is verythinly coated on the surface of the member 1, for example, the surfaceof a shadow mask on the electron gun side. The thickness of the coatingis l 2 microns. In this case, an organic binder burning away by the heattreatment may be mixed in order to raise the coating efficiency.

Subsequently, a liquid in which the particles 3 of the secondaryelectron emission preventing material of less than several microns inthe particle size are dispersed in water or ethyl alcohol is sprayed onthe coating by the conventional spraying method, for example, with aspray gun. Thus, the surface layer 12 is formed. A secondary electronemission preventing layer is composed of the surface layer 12 and themixed layer 2. The thickness of the surface layer 12 may suffice withseveral microns or more, and the upper limit is approximately 20 a.

In accordance with the forming method, the seeondary electron emissionpreventing layer is sufficiently strong in the bonding among theparticles and the bonding between the particles and the substrate, andcan satisfactorily endure practical use. Moreover, the secondaryemission ratio of the layer can be suppressed to a sufficiently smallvalue, since the inorganic binder of a large secondary emission ratioexists only in the vi einity of the member 1.

EXAMPLE 5 A mixed liquid containing potash water glass at aconcentration of %by weight and 6.6% by weight of flake graphite of aparticle size of l ,u. is sprayed on the surface of a shadow mask to athickness of approximately 1 to 2 by means of a spray gun, to form amixed layer 2. Subsequently, a liquid in which flake graphite particlesare dispersed in water or ethyl alcohol at a concentration of l to 10%by weight, practicaily 6 to 8% by weight, is sprayed on the mixed layerusing, for example, a spray gun, to form the surface layer. A secondaryelectron emission preventing layer is formed of the surface layer andthe mixed layer.

The secondary electron emission preventing layer thus formed, has asufficient strength. The secondary emission ratio is shown at a curve 26in FIG. 10, which is quite similar to the case of graphite alone with nomixed layer 2, and hence, an excellent secondary emission preventingeffect is exhibited.

The secondary electron emission preventing layer of the presentinvention has a great effect in improving a picture of thepost-deflection acceleration type color picture tube by applying it notonly to the shadow mask, but also to other components on which primaryelectrons impinge, for example, the inner wall of a glass bulb, a masksupport, a shield electrode and so forth.

As described above, the method of forming a secondary electron emissionpreventing layer for a postdeflection acceleration type color picturetube according to the present invention is very greatly effective inpractical use in that the bonding force of the particles of thesecondary electron emission preventing material is increased, that thestrength of the whole secondary electron emission preventing layer andthe adhesive force of the layer with the substrate can be increased, andthat the secondary emission ratio can be reduced as compared with thatof the prior-art secondary electron emission preventing layer employingthe inorganic binder.

What we claim is:

1. A method of forming a secondary electron emission preventing layerfor a post-deflection acceleration type color picture tube, comprising:forming a first layer of water glass at least on a surface at which theformation of secondary electron emissions is to be prevented in a colorpicture tube on an electron gun side, forming a second layer of anorganic binder containing graphite particles on said first layer, andthereafter burning away said organic binder in said second layer by aheat treatment, to form a secondary electron emission preventing layeron said surface.

2. The method according to claim 1, wherein said first layer is formedto a thickness of l to 2 [.L.

3. The method according to claim 1, wherein said second layer is formedto a thickness of 3 to 30 [.L.

4. The method according to claim 1, wherein said second layer is formedto a thickness of 5 to 10 a.

5. The method according to claim 1, wherein said graphite particles havea particle size of at most several microns.

6. The method according to claim 1, wherein fine powder of a materialwhich exerts no adverse influence on the picture tube is added to saidwater glass of said first layer.

7. The method according to claim 6, wherein said material exerting noadverse influence on the picture tube is one selected from the groupconsisting of graph ite and silver.

8. The method according to claim 1, wherein said first layer is of apotash water glass material which does not burn away by heat treatment.

9. The method according to claim 1, wherein said surface at which theformation of secondary electron emission is prevented in a color picturetube on the electron gun side is a surface of at least one of a shadowmask, the inner wall of the glass bulb, a mask support, or a shieldelectrode.

10. The method according to claim 1, wherein said surface is the surfaceof the shadow mask on the electron gun side.

11. The method according to claim 1, wherein said second layer contains6.6 percent by weight of flake graphite.

12. The method according to claim 1, wherein said flake graphite has aparticle size of 1 micron.

1. A METHOD OF FORMING A SECONDARY ELECTRON EMISSION PREVENTING LAYER FOR A POST-DEFLECTION ACCELERATION TYPE COLOR PICTURE TUBE, COMPRISING: FORMING A FIRST LAYER OF WATER GLASS AT LEAST ON A SURFACE AT WHICH THE FORMATION OF SECONDARY ELECTRON EMISSIONS IS TO BE PREVENTED IN A COLOR PICTURE TUBE ON AN ELECTRON GUN SIDE, FORMING A SECOND LAYER OF AN ORGANIC BINDER CONTAINING GRAPHITE PARTICLES ON SAID FIRST LAYER, AND THEREAFTER BURNING AWAY SAID ORGANIC BINDER IN SAID SECOND LAYER BY A HEAT TREATMENT, TO FORM A SECONDARY ELECTRON EMISSION PREVENTING LAYER ON SAID SURFACE.
 2. The method according to claim 1, wherein said first layer is formed to a thickness of 1 to 2 Mu .
 3. The method according to claim 1, wherein said second layer is formed to a thickness of 3 to 30 Mu .
 4. The method according to claim 1, wherein said second layer is formed to a thickness of 5 to 10 Mu .
 5. The method according to claim 1, wherein said graphite particles have a particle size of at most several microns.
 6. The method according to claim 1, wherein fine powder of a material which exerts no adverse influence on the picture tube is added to said water glass of said first layer.
 7. The method according to claim 6, wherein said material exerting no adverse influence on the picture tube is one selected from the group consisting of graphite and silver.
 8. The method according to claim 1, wherein said first layer is of a potash water glass material which does not burn away by heat treatment.
 9. The method according to claim 1, wherein said surface at which the formation of secondary electron emission is prevented in a color picture tube on the electron gun side is a surface of at least one of a shadow mask, the inner wall of the glass bulb, a mask support, or a shield electrode.
 10. The method according to claim 1, wherein said surface is the surface of the shadow mask on the electron gun side.
 11. The method according to claim 1, wherein said second layer contains 6.6 percenT by weight of flake graphite.
 12. The method according to claim 1, wherein said flake graphite has a particle size of 1 micron. 